There are many devices which have remote controls mounted at the end of a cable or the like, with the remote controls having switches to control the operation thereof. An example of this is the remote controlled hospital bed which typically has a hand control mounted at the end of a cable, with the cable extending to a control box beneath the bed. One or more motors, and their associated gearing as is known in the art, are used to control the position of the various parts of the bed. For example, one reversing motor may control the angle of the back of the bed with respect to the rest of the bed, another motor may be used to control the overall height of the bed from the floor, and still a third motor may be used to control the amount of angle formed between the bottom of the bed and the midportion of the bed at the knee.
For each motor provided, and each movement of a portion of the bed, there are generally two switches mounted in the hand control. One switch may be depressed to raise that portion of the bed being controlled, and the other switch used to lower that portion. Generally, the control circuit provides one wire extending between the control box and hand control which is electrically "hot", and one return wire for each switch contained in the hand control. Thus, for a two motor bed providing up and down movement for the back and the entire bed, four switches are mounted in the hand control and five wires extend between the hand control and the control box. Similarly, for a three motor bed providing up and down movement for three different portions of the bed, six switches are provided in the hand control and seven wires in the cable extending between the hand control and the control box.
The inventor herein has succeeded in designing a control circuit which eliminates one or more wires which must be included in the cable extending between the control box and the hand held remote control. This provides many advantages, including cost, ease of installation, increased flexibility of the control cable as a smaller number of wires need be contained therein for any number of functions, and additional features as will be described. Essentially, the new control circuit provides for the generation of a positive control voltage which is conducted along one wire, and a negative control voltage which is conducted along another wire from the control box to the hand held control. The negative voltage feeds all of the "down" switches, for example, for each direction of movement while the positive voltage feeds all of the "up" switches for all of the directions of movement. Additionally, one wire connects the outputs of each pair of switches for each function and returns to the control box. Thus, for a three function bed, the control cable includes only two wires carrying the positive and negative control voltage and three wires carrying the control signal from each of the three pairs of switches. For a three function bed only five wires need be included in the cable as opposed to the seven wires required in the prior art. In operation, as either switch is depressed for any function, the control voltage flows along the corresponding wire to the pair of LEDs connected in parallel and reverse polarity, each LED being opti-coupled with a photo emitting diode to trigger a photo sensitive triac to complete the circuit across the selected winding of the selected motor. Consequently, this solid state control circuit provides the significant advantage of reducing the number of wires which must be included in a control cable, and which provides other features and advantages more fully explained by referring to the drawings and the description of the preferred embodiment which follows: